A circuit of the above kind, a data carrier of the above kind and a communications device of the above kind are known from patent document WO 03/079281.
This document discloses a portable communications device, namely a mobile telephone, having a communication station configuration comprising a first communication stage for contactless communication with at least one data carrier external to the mobile telephone, and having a data carrier configuration comprising a second communication stage for contactless communication with at least one communications station that is also external to the mobile telephone. Provided in the mobile telephone is a detection circuit that is designed to detect the presence of an external data carrier or an external communication station in a communication zone of the communication station configuration incorporated in the mobile telephone and the data carrier configuration incorporated in the mobile telephone. Also provided is an activation circuit that cooperates with the detection circuit, the activation circuit being able, as a function of the result of the detection by the detection circuit, to activate the communication station configuration or data carrier configuration incorporated in the mobile telephone to communicate with their respective pendants. For communication to be established with the individual pendant—such as with a read/write station for example—the read/write station first emits a signal that represents an inventorizing command. This signal is processed by means of the circuits of the communication stages incorporated in the mobile telephone in such a way that the stages transmit their items of identifying information simultaneously, via their interfaces and their transmission means, to the read/write station. This will undoubtedly lead to what is termed a collision at a given bit position, and this collision will be recognized by the read/write station and dealt with by a so-called anti-collision procedure such as is defined in standard ISO 14443 for example. The collision occurs in this case at a physical level in the electromagnetic field between the read/write station and the communication station and becomes apparent in the form of at least one signal segment that is subject to a collision, which signal segment indicates the existence of two units of information that differ in respect of their information content and were transmitted to the read/write station simultaneously.
In the case of the known communications device, it has proved to be a disadvantage that both the communication station configuration incorporated in the mobile telephone and the data carrier configuration incorporated in the mobile telephone have to be provided with transmission means that are each arranged to transmit electromagnetic signals, and with interface means that are arranged to cooperate electronically with the transmission means, the interface means being arranged on the one hand to receive input information signals contained in the electromagnetic signals and on the other hand to transmit output information signals. It also has to be detected in the mobile telephone which of the two configurations needs to be activated, for which purpose, as mentioned, the detection circuit and the activation circuit are required. As a result, there are a very large number of components, some of which are redundant, and this increases the power consumption and size of the device.